Tether
by Cougar rolypoly bug
Summary: What actually happened between Sebastian and Jace during the two weeks that they were untraceable? What if Jace's blood also changed Sebastian as well? (I don't own the cover image)
1. Chapter 1

**Hey guys, I'm back with a new Fanfiction. **

**I'm not quite sure where this one is going, but it's basically going along the assumption of what happened during the two weeks when Sebastian and Jace were traveling around in the world in the apartment.**

**Please tell me what you think; the next chapter should be up pretty soon.**

**I do respond to comments.**

TETHER: Chapter 1-Lilith's Rune

Jace stood impatiently as he watched the glass coffin where Sebastian's corpse floated. It wasn't exactly that he expected the other boy to be able to do anything, but he knew better than to leave Sebastian alone just in case something was to happen because it seemed foolish to leave him alone after everything they had gone through.

_Come here_. Tether

The voice in Jace's mind was soft and tantalizing and it drew him in, but it was also painfully familiar.

Sebastian.

_Did you think you were free because Lilith is gone? The vampire's bite woke me; now her blood in my veins compels you._

_ Come here._

Jace felt it difficult to breathe all of the sudden. He was being suffocated.

He was being slowly pulled forward as he was forced to obey Sebastian's will and he did his very best to ignore the small part of his mind that just wanted to give in to his brother. The part of him that was still Valentine's son.

He did his best to dig his heels into the ground and fight against the invisible force that was dragging him forward towards Sebastian's coffin, but it was to no avail.

Jace bit his lip until he tasted blood, but still he wasn't in control of his body. He found himself looking down into the coffin where Sebastian floated in the clear liquid that was certainly not water, looking rather like a drowned corpse. His pale blonde hair floated around his face, almost completely colorless, and the lids of his closed eyes were blue. He looked, Jace thought, like a young version of Valentine.

Jace's hands began to rise completely against his will, even as he laid the edge of his dagger against his right palm.

His lips started moving quickly and he heard the words as if through water and even as he said the words he couldn't understand what he was saying.

He kept mentally screaming at himself to stop, but at the same time he couldn't stop no matter how hard he tried.

He let the knife come down against his palm. There was a clean shallow slice along his palm. The blood began to pool up in his palm.

Jace did his best to pull his hand back, but he couldn't move it. He watched in horror as his blood dropped onto Sebastian's pale face.

Almost instantly the boy's dark eyes shot open.

They were black, blacker than they had been before, darker than Valentine's. They were as dark as Lilith's, the demon who called herself his mother.

Sebastian's eyes reflected Jace's frightened face, twisted and unrecognizable.

Jace's blood was flowing more freely and he didn't make a move to stop the blood from dripping down his wrist and fingers, not that he could have had he wanted to.

Sebastian moved and the bloody water rippled around him as he sat up, trickling from him like rain. His pale, nearly colorless hair stuck to his forehead. He raised a hand and held it out to Jace, who held his dagger out blade first as Sebastian slid his hand along the length of the blade, not wincing as blood bloomed along the line on his palm. He pushed the knife away and took Jace's hand tightly.

That was the last thing Jace had expected, not that he could move away. He could feel each of Sebastian's icy fingers wrapped around his hand as he pressed their bleeding cuts together.

Jace tried to scream, but the cry died in his throat. He looked down at Sebastian's hand interlocked with his own as the blood ran through their fingers and down their wrists.

All of the suddenly a strange sense of peace came over Jace, even as it terrified him. How could he feel _so_ peaceful around Sebastian? Sebastian, who had killed Max, who'd killed Hodge, who'd tried to kill Isabelle, who'd knowingly kissed his sister, yet Jace felt like it was somehow right for them to be together.

Sebastian spoke again in his mind, but this time his voice was oddly welcome. It was comforting.

_We are one now, little brother, you and I, _Sebastian said.

_We are one._

Together the two boys stood overlooking the New York City skyline before Sebastian took Jace's hand again and twisted the ring on his finger as they both disappeared.

_Five minutes. _Clary had said that she'd be back in five minutes.

Maybe she would come back in those five minutes, maybe not, but either way, she would be returning to an empty room.

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	2. Chapter 2

**Hey guys! I'm back with chapter two! **

**So what did you guys think of the last chapter? **

**Did you like it? **

**Hate it?**

**Just not care half enough to say?**

**Please! Let me know what I can do to make it better!**

**Disclaimer: **_I don't own the Mortal Instruments or any of the characters that I'm using in this story, all rights go to the brilliant Cassandra Clare._

TETHER-Chapter 2-Identies Kept the Same

Jace was suffocating. He couldn't breath. He was used to the feeling of a portal swirling around him and making him feel like he was falling, and in some way this was similar, but at the same time, he could hardly breath. He was panicking. Jace Herondale was panicking.

And before he knew it, it stopped.

He could feel something cool beneath his fingers, cool and smooth.

He felt ill, as he knelt on the ground. No, he realized. He was kneeling on a cool wooden floor. He was indoors than.

The blood that had been on his hand was now dried and Sebastian's hand had been pried from his.

After an unknown amount of time Jace managed to look up to see Sebastian kneeling beside him, breathing hard.

"Sorry," Sebastian gasped. "That was harsher than I expected."

"It's fine," Jace said, raising his hand in a vague gesture that he was okay, though he still wasn't sure why he was acting so calm, so normal around Sebastian. He was a murderer, why hadn't Jace at least tried to fight him yet, because that was all he wanted to do, but he had no control over his own body.

Sebastian rose shakily to his feet and walked over to where Jace was kneeling.

"Brother, are you all right?" Sebastian questioned, a look of confused concern appearing on his pale face as he reached out hesitantly towards Jace and rested a hand on his shoulder.

"Just a bit dizzy." Jace nodded, shocked at the genuine smile that came with his words. He could list the people who could make him smile genuinely on one hand. Clary, Alec, Izzy, and now apparently Sebastian.

"Well that's good little brother," Sebastian said with what Jace would have called a relieved expression on anyone else, but how could _Sebastian _be relieved that _Jace_ was okay, the two boys hated each other and the last time they saw each other, Jace had killed Sebastian which would have put anybody of, but instead he offered Jace a hand to help him up, which he took after a moment's hesitation.

"I think a proper introduction is in order, I don't think that last time went all too well." Sebastian said with a small smile, referring easily to how Jace had killed him as he stood up straighter and held out a hand to Jace. "Hello, I'm Jonathan Christopher Morgenstern."

Jace smiled as well despite the lingering feel of wrongness. "I'm Jonathan Christopher…" He hesitated. Earlier he'd considered being a Herondale but, he'd be raised thinking he was a Wayland, and the man who'd brought him up until he was ten, the an that he'd considered his father was a Morgenstern, but he'd been truly accepted as himself by the Lightwoods, so which name was truly his own.

"You're going to have to pick a last name." Sebastian grinned as if sensing his inner struggle.

"I suppose Morgenstern is already taken?" Jace said coolly.

"Indeed. I was Jonathan Morgenstern first, therefore I get to keep my own name." Sebastian replied with a glint in his black eyes.

"Herondale." Jace said, the name slipping from between his lips before he could stop it, almost against his will. "My name is Jonathan Christopher Herondale."

"Well that won't work, we can't both be Jonathan Christopher." Sebastian pointed out. "What would you like to change your name to?" Sebastian questioned, his voice shockingly kind.

"Why me? Why aren't you changing your name?"  
"Because I was born first." Sebastian stated without any doubt that he would have his way. "I am Jonathan Christopher Morgenstern. I am Valentine's son."

"But I—" Jace hesitated, his voice shaky and he was shocked to realize that he felt betrayed. "You called me brother. Aren't I?"

Sebastian dark eyes widened slightly as he gazed questioningly into Jace's golden eyes. "And we are brothers, in everyway that matters. We are brothers in more than blood, we are once Jace Herondale, and we are bound together. You are _my_ brother!" Sebastian started off softly, his words easy and controlled, but as we went on his words became frantic until his voice rose to a desperate, delighted shout, yet Jace wasn't at all scared by Sebastian's desperate tones, even if a nagging voice at the back of his mind was telling him that he should.

"Jace."

"What?" Sebastian asked, his expression scrunching up in confusion.

"You told me to pick another name. I pick Jace. Not Jonathan, Jace."

"Well than Jace, I'm Jonathan Christopher Morgenstern," He hesitated, looking uncomfortable.

"Jonathan? What's wrong?" Jace questioned, watching the other boy with concern of his own. The name felt strange on his tongue. It was odd addressing somebody else by your own name.

He cleared his throat. "I'm Jonathan—" He tried again, before grimacing at the floor.

"I'm Jonathan Morgenstern!" He cried, his black eyes wide. Something was clearly very wrong.

"Are you sure about that?" Jace asked, his tone light and mocking.

"Shut up Jace," Sebastian snapped before taking another breath.

Jace could feel Sebastian's tension and irritation, but for some reason he wanted to comfort him.

"I don't know who I am." He said, his voice strange and childlike. "Valentine named me Jonathan Christopher and called me by that name my entire life, but he also named you Jonathan Christopher. We have the same name; it's never been mine. I've never felt like a Jonathan and now I don't have to be him. I can be whoever I want."

"Okay…" Jace hesitated. "Than what name are you taking?"

"Sebastian." He said, this time seeming more at ease as he said the name. "I will take the name Sebastian. It was just a lie when I was pretending to be Sebastian Verlac, but I have taken a certain liking to that name, so I will keep it."

"Very well, Sebastian." Jace grinned.

"Jace and Sebastian." Sebastian said with a nod of approval. "Not much of a change here, now is there?"

"Not much at all." Jace replied, not missing the delighted look on Sebastian's face, or the way his black eyes glinted maliciously, not unlike Valentine's used to when he was still alive.

"Now come brother, you seem tired, sleep and when you wake we will take the world as ours. All shall bow before the force that is Valentine's children. We will never be denied anything ever again. We will be able take what we want when we want it."

Jace didn't say anything as Sebastian led him to his room.

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**Next chapter should be up soon!**


	3. Chapter 3

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**Two chapters in one day!**

**Because, well, why not!**

**Please tell me what you thought!**

_I DON'T OWN ANYTHING!_

TETHER-Chapter 3-Alone

Jace stood in front of the door to Sebastian's bedroom. He knew it was past the time that they should have started training, but Sebastian was still asleep, or at least he hadn't left his room.

Before, Jace would have been terrified to go into Sebastian's room, even if he was still asleep and in a way, Jace was still scared. Not that Sebastian would hurt him, but of what he might see.

Jace was shocked that when he opened the door he was met with the bedroom of a teenager. The room was in a state of disarray that could not be replicated by anybody as obsessive as Jace and couldn't be avoided by someone ask typically careless, in the way that teenagers are expected to be, as Sebastian. Overall, the room wasn't unlike Alec's back at the New York Institute.

"Sebastian!" Jace called, clapping his hands.

The other boy woke suddenly, sitting straight up, his dark eyes wide and panicked and his white blonde hair sticking up messily in every direction. This was the first time Jace had seen him looking anything less than composed and he would have been lying if he claimed that he didn't take any pleasure from seeing him so bedraggled.

"Jace," the older of the two sighed, relief flooding his expression.

"Morning, Sleeping Beauty." Jace teased. "How did you sleep, big brother?"

"Fine," Sebastian mumbled, running a hand through his hair, making it stick up even more than it had before, but Jace hadn't missed the way that he wouldn't meet his eyes or the unusual nervousness he was feeling, as he struggled to keep his breathing even, though he had no idea why. "Do you want to go and train?"

Sebastian fell back against his pillows in a hopeless attempt to fall asleep again. Despite the careless and relaxed way he fell back and appeared, Jace seemed to notice that he was faking the ease with which he sat. The small smile that rested on his lips faltered ever so slightly and he was breathing too quickly to be as relaxed as he was playing at being.

Jace was shocked that he could realize the other boy's tells, but at the same time, he knew how he could. Because their tells were the same, and the way that Sebastian was trying to hide his true emotion was exactly the same as the way Jace hid fear and pain behind jokes and laughter. Another reminded that the same man had brought them up, trained the same way.

"What's wrong Sebastian?" Jace asked.

He opened his eyes quickly looking up at Jace, shocked that he had realized that anything was wrong. Not many people could see through him so easily, but at the same time he was delighted that somebody knew him well enough to know that he was lying.

Jace didn't expect Sebastian to answer, he certainly wouldn't have, but after a moment's hesitation he did.

"Clarissa." He said so softly Jace wasn't sure if he'd actually spoken.

"Clary? What about her?" Jace asked, aware to the way his stomach twisted at the thought of his girlfriend. She had no idea where he was; she had no idea if he was okay, or if he was even alive.

Somehow he knew that Sebastian could sense his emotions, considering how he looked away, looking almost guilty. Maybe with the rune that bonded they could feel the other's emotions, he would have to ask Sebastian about that later, he decided.

"She thinks that I kidnapped you, Jace." He pointed out, covering his eyes with his arm. "She'll think I forced you to come with me, she'll hate me. She already does."

Jace didn't bother to ask how he knew this, he knew that Clary hated Sebastian, he'd heard her say it countless times, before and he'd always agreed, but now, seeing him looking so miserable, he wished that there was a way that the three of them could live together and the three of them could be happy. Surely if Clary realized that Sebastian hadn't hurt him, than she would forgive him for…what was it that he'd done wrong again? It mustn't have been that bad if Jace couldn't even remember.

"Why don't we bring her to stay with us?" Jace suggested.

Sebastian's demeanor brightened instantaneously as he sat up and grinned at Jace. "Do you really mean it?" He asked, desperately excited. "You'd be okay with us going to bring her back with us?"

"Well, we'd give her a choice of course…" Jace added tentatively.

"But we could bring her back here with us?" Sebastian repeated.

"She is my girlfriend Sebastian, I would like to be able to see her." Jace said, straight-faced before they both burst into laughter. Jace didn't laugh like that with many people.

"Do remember that she's _my_ little sister." Sebastian pointed out.

"Of course," Jace agreed. "I would have thought you would be delighted that she's dating someone as gentlemanly as me."

A flash of something appeared and disappeared from his expression before Jace could identify it. "Of course, however, it is my job to protect her."

"Are we going to train or not?" Jace asked.

"Of course, I'll meet you in the training room, I'll assume you know where it is?" Sebastian asked.

"Yeah," Jace replied, slightly confused as to how he knew exactly where the training room was.

"I'll meet you there in a few minutes." Sebastian repeated as Jace headed out of the bedroom and to the training room.

Only after he was sure Jace had left did Sebastian go to his dresser and pick up the silver box. He ran his fingers carefully over the initials on the top of the lid. _His_ initials.

He'd long since memorized the contents. A few strands of his baby hair, a few photos, a baby shoe…pieces of the life that he could have had if his mother hadn't been such a coward, if she hadn't run, leaving him alone with Valentine. How could she not know how cruel his father would be to him in her absence, but Sebastian had long ago realized that his mother could have very well known just what Valentine would do to him and just didn't care.

He ran his fingers gently over the items in the box before closing it carefully and going to change into training gear.

Before heading to the training room, he gave the silver box one last look as he willed a small smile onto his lips.

_Clarissa_, he thought to himself. _We're coming to get you, to save you from _her. _We're coming to save you from your mother._

With that thought in mind he went to join Jace in the training room.

**So what do you guys think? Should I continue with this story? Yes? No?**

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**Next chapter should be up soon!**


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